Fluidized bed for heat-treating purposes



Aug.4, 1970 H. GElPEL ET Al, 3,522,936

FLUIDIZED BED FOR HEAT-TREATING PURPOSES Filed Feb. 12, 1968 EECUNOI 7' ONING' CHAMEEQ United States Patent 3,522,936 FLUIDIZED BED FOR HEAT-TREATING PURPOSES Hans Geipel, Oberhausen-Sterkrade, Eckenhard Forster,

Oberhausen, and Wilfried Heinemann, Duisburg-Hamborn, Germany, assignors t0 Huttenwerk Oberhausen AG, Oberhausen, Germany, a corporation of Germany Filed Feb. 12, 1968, Ser. No. 704,956 Claims priority, application Germany, Feb. 10, 1967, H 61,811 Int. Cl. C21d 9/56 US. Cl. 2663 5 Claims ABSTRACT OF THE DISCLOSURE Goods to be heat-treated, e.g. coils of steel wire to be subjected to controlled cooling, are placed on an apertured conveyor passing through a tunnel into which solid ceramic particles entrained by a stream of carrier gas are admitted through a perforated base below the conveyor, the particles enveloping the conveyed goods and being then recirculated through a heating or cooling chamber restoring their original temperature. In order to minimize loss of particles at the entrance and exit ends, the gas is blown in at a relatively high rate throughout a central portion of the base and at a sharply throttled rate near the ends whereby the particles accumulate in a stepped pile; the inlet and outlet ports for the conveyor are disposed at a level above the top of the lower end portions but below the top of the higher middle portion of that pile so that the goods traverse only this middle portion.

Our present invention relates to a fluidized bed for the heat treatment of workpieces, particularly but not exclusively for the cooling of steel wire which is to be patented (i.e. cooled at a controlled rate) for transformation from its austenitic state to a sorbitic pearlite structure as more fully disclosed in our commonly owned application Ser. No. 675,522 filed Oct. 16, 1967.

The term fluidized bed denotes a mass of solid particles, such as ceramic granules, entrained by a current of 9. preferably inert carrier gas. The particles, which should have an elevated heat-transfer coeflicient, serve as the principal constituent of the heating or cooling medium whereas the carrier gas plays only a minor role in the maintenance of the desired discharge temperature. This gas is also used as a vehicle for a continuous recirculation of the particles through a heat-treating tunnel and through an external reconditioning chamber where the particles are reheated or recoded to re-establish their original treatment temperature.

One of the poblerns encountered in such systems is the continuous loss of particles through the inlet and outlet ends of the tunnel, especially the latter, which must give clearance to the goods and to a conveyor carrying same. In the system described in our copending application identified above, this loss is minimized by the provision of exhaust ducts above and below the apertured conveyor in the vicinity of the outlet port of the tunnel. In another copending application of our also filed Oct. 16, 1967,

er. No. 675,426, now abandoned, we have disclosed the use of an auxiliary conveyor disposed underneath the principal conveyor near the discharge end, the auxiliary conveyor rotating in reverse direction to impede the outward entrainment of particles by the principal conveyor.

The general object of our present invention is to provide alternative means, without the use of additional moving parts, for avoiding substantial leakage of such particles from the heat-treating tunnel while allowing ex- 3,522,936 Patented Aug. 4, 1970 act predetermination of the contact time between the particles and the goods.

A more specific object of this invention is to provide means in such system for concentrating the treatment particles in a pile of well-defined and substantially stationary outline spaced from at least the outlet port and preferably also from the inlet port of the tunnel.

If the particles are allowed to accumulate in random fashion to a certain level from which the conveyor carrying the goods emerges in an upwardly inclined direction, outward entrainment by the conveyor will also be minimized but the contact time between the goods and the particles will vary with distance from the conveyor surface. Thus, if the goods are relatively tall or are stacked on the conveyor, their treatment will not be uniform. To avoid this drawback, our invention further aims at providing means for allowing the conveyor to pass approximately horizontally through a fluidized bed with substantially vertical boundaries spaced from the inlet and outlet ports of the tunnel.

These objects are realized, pursuant to our present invention, by a circulation system for the treatment agent which causes the gas stream to pass upwardly through the tunnel from a perforated base underneath the conveyor, the system including pneumatic control means for concentrating the gas flow in a region of the tunnel spaced from the outlet port and preferably also from the inlet port. According to a more particular feature of our invention, the pneumatic control means may take the form of one or more valves for sharply throttling the flow rate near the exit end (and advantageously also near the entrance end) of the tunnel so that the bulk of the particles accumulates in a pile rising from the base above the conveyor level throughout an area which extends over the major part of the length of the conveyor inside the tunnel but stops short of its outlet port and preferably also of its inlet port.

We have found that admission of the gas stream to the base by way of an underlying manifold, subdivided by transverse partitions into a main central section and two relatively short terminal sections, will give rise to a particle pile with well-defined steps above the partitions if the flow rate through the terminal sections of the manifold is throttled in the aforedescribed manner with reference to the flow rate through the central section. Thus, we may establish a pile rising to a predetermined level above the conveyor throughout the region overlying the central manifold section and dropping to a level well below the conveyor above the terminal sections thereof; with proper selection of flow rate and total volume of recirculated particles, the pile may rise at its center to about twice the distance of the conveyor from the base and at the end to roughly 30% of this height so as to leave an appreciable clearance between the top of the pile and the conveyor in the vicinity of the ports.

The spacing of the particle accumulation from the entrance end of the tunnel will be particularly desirable where the goods are deposited on the conveyor before the latter enters the tunnel.

The invention will be discussed in greater detail with reference to the accompanying drawing whose sole figure diagrammatically represents, in longitudinal section, a system embodying our present improvement.

The system shown in the drawing comprises an apertured conveyor 4, in the form of an endless belt such as a wire netting or a set of parallel wires, mounted on a pair of rollers 14', 14" which are driven by a motor not shown to advance the conveyor in the direction indicated by arrow A, i.e. with its upper run moving from right to left. This upper run traverses an elongated tunnel 3 having an inlet port 5 and an exit port 6 at approximately the same level. A perforated base 15 within tunnel 3, disposed underneath the upper conveyor run, is spaced from the tunnelbottom to define therewith a manifold for the circulation of a treatment agent of the aforedescribed character, i.e. a stream of gas entraining a mass of solid particles 2 (e.g. of magnesia). Circulation is effected by means of a blower 16 in a conduit 17 which also includes a reconditioning chamber 18, i.e. a cooling chamber if the goods to be treated are coils of steel wire to be patented. These coils, indicated at 1, are deposited on the conveyor 4 at a location 19 upstream from tunnel 3, advantageously with the aid of a transversely oscillating dispenser as disclosed and claimed in our commonly owned copending application Ser. No. 675,405 filed Oct. 16, 1967. Conduit 17 communicates by way of respective branches 17a, 17b, 170 with sections 9, 10, 11 of the manifold bounded by base 15, these sections being formed by a pair of transverse partitions 7 and 8. The main manifold section underlies a central portion of base extending over the greater part of the length of the tunnel; the two terminal sections 9 and 10 underlie relatively short portions of the base in the region of the outlet 6 and the inlet 5, respectively. To complete the pneumatic circuit, gas and solid particles 2 are exhausted from tunnel 3 and returned to chamber 18 via a duct having branches 20a, 20b, 200.

In accordance with an important feature of our invention, the branches 17a, 17b, 170 are provided with respective valves 21a, 21b, 216 so adjusted that the flow rate through manifold sections 9 and 11 is sharply throttled in comparison with the rate of flow through central section 10. Further flow control may be achieved with the aid of valves 22a, 22b, 22c in branches 20a, 20b, 20c, respectively.

With the arrangement illustrated, the bulk of the particles 2 accumulates above manifold section 10 on base 15 in a pile having a substantially uniform depth d, the pile being sharply stepped at 12 and 13 (Le. above partitions 7 and 8) down to a height which is well below the level of the goods 1 and which may be equal to approximately 0.3d while the elevation of the conveyor above base 15 is about 0.5d. With the ports 5 and 6 thus located above the pile surface, few if any particles 2 will leave the tunnel by either port. As the distance between steps 12 and 13 is Well defined by the separation of partitions 7 and 8, the residence time of the goods in the pile of particles 2 can be readily predetermined. If desired, the operating temperature of chamber 18 and/ or the speed of conveyor 4 may be varied in response to measurements of the temperature of the goods at the exit port 6 as described in our aforementioned copending application Ser. No. 675,522.

Surprisingly, if the flow through branches 17a and 17c is cut off completely, the boundaries of the pile of particles 2 accumulating on base 15 will be less sharply defined than under the aforedescribed operating conditions in which a limited accumulation is allowed to take place near the ports 5 and 6.

We claim:

1. A fluidized bed for the heat treatment of workpieces, comprising an elongated tunnel with an inlet port and an outlet port disposed at opposite ends thereof and substantially at the same level;

an apertured conveyor passing through said tunnel by Way of said inlet and outlet ports;

a perforated base in said tunnel underneath said conveyor; circulation means for blowing a treatment agent upwardly through said base into said tunnel and withdrawing said treatment agent from said tunnel for reconditioning, said treatment agent consisting of a gas stream with entrained solid particles;

and pneumatic control means for concentrating said gas stream in a region of said tunnel spaced from said outlet port with accumulation of said particles on said base in a pile which extends above said conveyor over the major part of its length within the tunnel while letting the conveyor emerge from said pile at a location upstream from said outlet port.

2. A fluidized bed as defined in claim 1 wherein said pneumatic control means is arranged to maintain said pile also spaced from said inlet port.

3. A fluidized bed as defined in claim 1 wherein said circulation means includes a manifold underneath said base and partition means dividing said manifold into a main section underlying a major part of said base and at least one terminal section underlying a minor part of said base adjacent said outlet port, said control means including valve means for sharply throttling the flow rate of said gas stream through said terminal section with reference to the flow rate through said main section.

4. A fluidized bed as defined in claim 3 wherein said manifold is further divided by said partition means into another terminal section underlying a minor part of said base adjacent said inlet port, said 'valve means being operative to maintain a substantially identical flow rate through both said terminal sections.

5. A fluidized bed as defined in claim 4 wherein said flow rates are so chosen as to make the height of said pile above said terminal sections equal to approximtaely 30% of the height above said main section.

References Cited UNITED STATES PATENTS 2,971,242 2/1961 Doleman et al.

2,995,773 8/ 1961 Gidlow et al.

3,355,159 11/1967 Ayers 2663 3,390,871 7/1968 McLean et al. 148-l56 X 3,391,915 7/1968 Morgan 266-3 3,445,100 5/1969 Bond 2663 I. SPENCER OVERHOLSER, Primary Examiner R. S. ANNEAR, Assistant Examiner U.S. C1. X.R. ll8-405 

